The invention relates to a fluid friction clutch with a primary part which includes a driving disk, and a secondary part which includes a housing. The primary and secondary parts are rotatably supported for rotation with respect to one another and the driving disk is arranged to rotate in a working space in the housing. By means of an intermediate disk secured to the housing, the working space is separated from a fluid storage space formed in the housing. At least one outlet or return bore is provided at the outer circumference of the intermediate disk for connecting the working space with the storage space. The viscous clutch fluid is guided from the working space to the storage space through the return bore or bores. A baffle member, which takes an end position in dependence upon the driving direction of the driving disk, serves to damm-up the clutch fluid in front of the return bore or bores to increase the return pressure.
By way of background information as to the type of clutch the invention relates to, see commonly assigned U.S. Pat. No. 4,278,158 to Martin.
With fluid friction clutches there is a problem to return pump the clutch fluid which flows from the storage space to the work space, back into the storage space. The return guidance normally occurs over channels which extend from the radial outer region of the working space to the storage chamber or space. In order to guide the clutch fluid, which because of the centrifugal force extends in these outer radial regions of the working space, with sufficient pressure to the return bores, it has been contemplated to damm-up the fluid in the region of the return bores with the help of baffle members. For example, see the above noted U.S. Pat. No. 4,278,158. With a known construction a roller is arranged radially outwardly of the driving disk between the same and the housing, which roller is shovable or moveable in the circumferential direction between two protrusions provided on the housing. In dependence on the rotational direction of the driving disk, the roller automatically takes one of two possible end positions in which it serves to damm-up the clutch fluid in front of the return bores. A disadvantage of this arrangement is that the roller is in direct friction contact with the driving disk, the housing wall and the housing protrusions, whereby wearing occurs. This results in that the amount of the clutch fluid which is pumped out for a given rotational speed decreases over time so that the control characteristics of the clutch are changed. Therefore new rollers must be inserted at certain intervals, requiring the disassembly of the clutch, and consequent expenditure of time and money.
According to another contemplated construction (Viskokupplung Saab Scania T 20 mul/edul), an annular groove is provided in the driving disk, in which a floating baffle member is disposed. The baffle member is moveable within limits in the circumferential direction of the driving disk, whereby the respective end position of the baffle member is established by means of limits stops arranged on the intermediate disk. The return bores extending in the axial direction of the intermediate disk are so arranged that they are respectively opened when the baffle member reaches one of its end positions. By this known construction, friction contact between the driving disk and the baffle member can occur because the baffle member can come into contact with the driving disk. However, the baffle member is stopped on the stop pins or protrusion in the circumferential direction. It is however disadvantageous with such a construction in that the driving disk must have a relatively large axial width in order to accommodate a baffle member of a correspondingly large axial width and reliably guide the same therein. This is contrary to the general present day tendancy to construct fluid friction clutches, especially for passenger automobiles, with as small a construction thickness as possible. Furthermore, the construction and material expenses for such driving disks are relatively large.
The invention is based upon the problem of avoiding the above-mentioned disadvantages and providing for the attachment of a baffle member for a fluid friction clutch, which is independent of the driving or intermediate disk thickness, so that the attachment of same with very thin driving and intermediate disks is possible, whereby the entire construction depth or thickness of the fluid friction clutch is minimized and furthermore constant clutch operating characteristics are guaranteed.
The invention contemplates the provision of a circumferentially extending guide at the intermediate disk for guidance of the baffle member to have limited movement in the circumferential direction and no movement in the radial direction. Such a guidance, which is preferably in the form of an oblong hole, can be simply and economically constructed independently of the axial depth of the intermediate disk. Thus the invention is especially advantageous if the fluid friction clutch should only utilize a very small construction depth or thickness. Therefore, because the baffle member is guided in the oblong hole, it is assured that its position is fixed in the radial direction and it does not rub or slide on the driving disk. A similar operation over a long period of time is therefore assured because no mechanical rubbing and therefore no wearing of the baffle member occurs.
In advantageous embodiments of the invention, it is contemplated that the baffle member is provided with a guidance pedestal which protrudes through the oblong hole of the intermediate disk into the storage space and that the baffle member is secured to the intermediate disk by means of an axial securement of the protruding pedestal part at the storage space side surface of the intermediate disk. By these means the baffle member is positioned in the axial and the radial direction so that it is moveable only in the circumferential direction to its two end positions in dependance on the relative turning direction of the driving disk and the housing. This arrangement has the advantage that the bearing support of the baffle member is basically unchanged for the two rotational directions, thus increasing the reliability of the regulation of the clutch. For the axial securement of the baffle member a retaining washer is used, which exhibits a cut-out and can be clamped over the protruding part of the guidance pedestal. One can also use snap rings (splined) or other known fastener elements according to other preferred embodiments of the invention.
According to a particularly advantageous embodiment of the invention, it is provided that two return bores are provided in the intermediate disk at the same radial distance from the center of the intermediate disk and separated from one another in the circumferential direction by means of a bridging part extending approximately one-twentieth (1/20) of the intermediate disk circumference. The baffle member exhibits a length in the circumferential direction corresponding to the distance between the centers of the return bores, and the radial height of the baffle member and the sliding movement thereof is so dimensioned that, in the respective end positions, one of the return bores and the oblong hole are closed by the baffle member. A particularly simple construction is provided when the oblong bore extends between the two return bores in the intermediate disk. With this arrangement the entire radial height of the baffle member can be minimized so that the baffle member can be constructed with a minimum of material.
According to especially preferred embodiments of the invention the circumferential ends of the baffle member (fluid damming surfaces) are beveled to increase their damming efficiency.
According to another preferred embodiment a return bore is formed through the intermediate disk and the oblong guidance hole is provided at a radial distance from the return bore. The baffle member exhibits a protruding part with which the clutch fluid is dammed and a part which covers the oblong hole in all possible positions of the baffle member. This embodiment offers the advantage that only one return bore must be formed in the intermediate disk, however the radial extension of the stop body must be greater than with the embodiment with two return bores because the oblong hole must be radially offset with respect to the return bore.
Yet another preferred embodiment is contemplated which utilizes the circumferential end regions of the oblong hole as the respective return bores, wherein the baffle member exhibits a correspondingly smaller length than the oblong hole, so that in respective ones of the baffle member end positions, there is a free region of the oblong hole through which the clutch fluid is guided to the storage space.
In all embodiments, the end regions of the baffle member may be provided with cut-outs to improve the guidance of the clutch fluid to the return bores.
The baffle members are preferably formed out of injection molded plastic, whereby they are very economically constructed. This is especially possible with the arrangements of the present invention because the baffle members will not experience any mechanical friction or rubbing and therefore they need not be especially stably constructed.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.